Confusing documentation on MathJax in light of use in Jupyter notebook

[embray]

As pointed out to me in ​this issue, ​this documentation page is a little confusing as to how use of the MathJax class relates to displaying LaTeX representations in the Jupyter notebook.

This confusion is increased by the fact that Jupyter doesn't display objects' latex repr by default (I'm not sure if that's the case or not for the classic Sage NB to which these docs were likely written). The user was confused into believing that the repr of a MathJax object should actually be rendered, and not display the raw HTML.

This section should probably be rewritten since it's confusing usage instructions with implementation details that won't be interesting to a casual user. I think these examples of using the MathJax class should be removed and/or moved to the class's API documentation (which could perhaps be linked to, but not further discussed?)

[embray]

Retargeting some of my tickets (somewhat optimistically for now).

[embray]

Removing most of the rest of my open tickets out of the 8.7 milestone, which should be closed.